U.S. Published Application 2005/0020926 discloses a scanned beam imager that may be used in applications in which cameras have been used in the past. In particular it can be used in medical devices such as video endoscopes, laparoscopes, etc.
The scanned beam imager disclosed in the published application has an illuminator that creates a first beam of light and a scanner that deflects the first beam of light across a field-of-view (FOV). The scanned beam of light sequentially illuminates spots in the FOV corresponding to various beam positions. While the beam illuminates the spots, the illuminating light beam is reflected, absorbed, scattered, refracted, or otherwise affected by the object or material in the FOV to produce scattered light energy. A portion of the scattered light energy travels to detectors that receive the light and produce electrical signals corresponding to the amount of light energy received, which is then converted to separate electrical signals. The electrical signals pass to a controller that builds up a digital image and transmits it for further processing, decoding, archiving, printing, display, or other treatment or use.
One example of the scanner employs a MEMS device carrying a reflector capable of deflection about two orthogonal scan axes, in which the reflector is driven in both scan axes at a frequency near their natural mechanical resonant frequencies. In another example, one axis is operated near resonance while the other is operated substantially off resonance. For completeness it is also noted that scanners are also know that employ two reflectors, one of which oscillates sinusoidally and the other of which simply scans linearly.
In a resonant scanner, the scanning reflector or reflectors oscillate such that their angular deflection in time is approximately a sinusoid, at a mechanical resonant frequency determined by the suspension stiffness and the moment of inertia of the MEMS device incorporating the reflector. Motion can be sustained with little energy and the devices can be made robust when they are operated at the mechanical resonant frequency. However, sinusoidal angular deflection is less than optimal for certain applications. The varying velocity inherent in a sinusoidal scan gives varying “exposure” at a given point in the FOV. This “exposure” is related to the power of the beam of the scanning beam imager, and its velocity, which varies over the FOV. The extremes occur in the center of the scan where the beam angular velocity is at its greatest and at the edges of the scan where the beam slows to reverse its direction across the FOV. Therefore, there is a need to modulate the power of the beam in a resonant scanning beam assembly to achieve a desired exposure at any specified part of the FOV.